1. Filed of the Invention
The present invention relates to a process for concentration and separation of an eicosapentaenoic acid ester based on the difference in affinity of highly unsaturated fatty acid esters for zeolites.
2. Description of the Prior Art
Eicosapentaenoic acid (hereinafter abbreviated as EPA) is a kind of highly unsaturated (or poly-unsaturated) fatty acid, which is commonly contained in fish oils, etc. EPA is an important substance as a precursor of prostaglandin and has been used as a nutritious additive for foods and the like. It was recently found that EPA was effective for various diseases, including blocking arteriosclerosis, and the like, and hence its demand as a medicine has been increasing quite rapidly.
In order to utilize EPA as a medicine, it must be separated from a mixture of fatty acids containing EPA up to a purity of at least 90%. Hitherto known processes for concentrating and separating unsaturated fatty acid esters, such as EPA ester, from their mixtures include a urea complex method (see British Patent No. 1240513) and a silver complex method (see the same patent), as well as an enzyme method, low temperature fractional crystallization methods, supercritical fluid extraction method, molecular distillation method, and the like. However, many problems arise with regard to purity, cost, operation, etc., when these methods are applied to concentration and separation of an EPA ester from a mixture of fatty acid esters containing the EPA ester, and therefore it is hardly possible to obtain highly pure EPA ester on an industrial scale. In Japanese Patent Application (Laid Open) No. 67,245/84 is disclosed a process for concentrating and separating an EPA ester and a docosahexaenoic acid ester, using a zeolite having a pore size of 5 to 13 .ANG.. In this case, too, it is hardly possible to obtain the EPA ester having a purity of 90% or higher.